Optical properties of Ag/dielectric-material multilayers

Abstract

Abstract The optical properties of the silver/dielectric-material multilayers have been investigated and it was found that the absorption exists at the silver/dielectric-material interfaces and is caused by the excitation of the surface plasmons of silver generated in the vicinity of the interface. In order to analyze the silver/dielectric-material interface, we prepared the silver layers overcoated with thin dielectric-material, whose thicknesses are less than the escaping depth of photoelectrons. X-ray photoelectron spectroscopy surface analysis on this two-layer stacks makes it possible to observe the oxidation state of silver and the surface plasmon of silver around the interface between the silver and the dielectric layer. The plasmon loss peaks of silver were observed to shift, depending on the dielectric constant of overcoating layers, TiO2, SiNx, ZnO and SiO2; these peaks shift largely with TiO2 overcoat and shift less with SiNx or ZnO overcoat. SiO2 overcoat makes almost no peak shift. Namely, the resonance energy of surface plasmons decreases and reaches to visible region with the increase of the dielectric constant of overcoating layer. These results are consistent with the fact that a larger absorption is observed in the stacks overcoated with a layer having a higher dielectric constant.